There is disclosed an electric steering column device of this type including a male screw shaft member rotatably supported by any one of a fixed side bracket and a movable side bracket, and a female screw member provided to the other one of the fixed side bracket and the movable side bracket and threadedly engaged with the male screw shaft member. The electric steering column device is configured to perform positioning of a steering shaft in a tilting direction and a telescopic direction by moving the fixed side bracket and the movable side bracket relative to each other in such a way that the female screw member is moved in an axial direction of the male screw shaft member with rotation of the male screw shaft member driven by an electric motor. However, the above-described electric steering column device needs to have a clearance (backlash) for sliding at a portion where the male screw shaft member and the female screw member threadedly engage with each other, and this clearance causes backlash of the steering shaft. Accordingly, there are proposed electric steering column devices which are capable of preventing a backlash between the male screw shaft member and the female screw member (see Patent Literature 1 and Patent Literature 2, for example).
As shown in FIG. 1, a steering column device 100 described in Patent Literature 1 includes a male screw shaft member 101 and a female screw member 102, and the female screw member 102 and a boss 103 are integrally formed. The boss 103 includes a housing hole 104 where to house a pressing member 105 pressing an outer peripheral surface of the male screw shaft member 101 in a direction of an internal diameter of the female screw member 102, a coil spring 106 biasing the pressing member 105 toward the male screw shaft member 101, and an adjustment screw 107 screwed in the boss 103 to adjust a biasing force of the coil spring 106.
In the above-described configuration, the adjustment screw 107 housed in the housing hole 104 of the boss 103 is appropriately adjusted by screwed toward the pressing member 105 so as to allow the pressing member 105 to press the outer peripheral surface of the male screw shaft member 101 in the direction of the internal diameter of the female screw member 102 by using the biasing force of the coil spring 106. Hence it is possible to prevent a backlash between the male screw shaft member 101 and the female screw member 102 and thereby to reduce a backlash of the steering shaft after positioning.
As shown in FIG. 2, a steering column device 110 described in Patent Literature 2 includes a female screw member 115 provided with three nuts 112, 113, and 114 that are separated from each other in an axial direction of a male screw shaft member 111. The intermediate nut 112 is provided with a female screw portion 112a formed on an inner periphery thereof to be threadedly engaged with the male screw shaft member 111, and is provided with ring-shaped outer peripheral protruding portions 112b and recessed portions 112c respectively formed in both ends thereof in an axial direction of the male screw shaft member 111. The recessed portions 112c are located at inner side of the outer peripheral protruding portions 112b in the radial direction, and disc springs 116 are housed in the recessed portions 112c. Annular fixation rings 117 and 118 are respectively fastened on the outer peripheral protruding portions 112b by use of fastening bolts 119, and female serrations (not shown) extending in the axial direction of the male screw shaft member 111 are formed on inner peripheries of the respective fixation rings 117 and 118. Female screw portions 113a and 114a to be threadedly engaged with the male screw shaft member 111 are formed on inner peripheries of the end nuts 113 and 114, and male serrations 113b and 114b to be firmly fit to the respective female serrations are formed on outer peripheries of the end nuts 113 and 114. In this way, the end nuts 113 and 114 can move relative to the respective fixation rings 117 and 118 in the axial direction of the male screw shaft member 111.
In the above-described configuration, a backlash between the male screw shaft member 111 and the end nuts 113 and 114 is eliminated by expanding clearances between the intermediate nut 112 and the end nuts 113 and 114 by use of the disc springs 116, and thereby backlash of the steering shaft is reduced.